Traction apparatus

ABSTRACT

A traction apparatus ( 1 A) includes at least one traction member ( 51 ) which engages a surface ( 10 A) against which traction is to be provided. The traction member can move relatively freely in one direction over the surface but has high resistance to movement in the other direction. The apparatus can be made to move by having a number of traction members ( 5156 ) which move or oscillate relative to each other. There are preferably a large number of traction members which are in the forms of bristles in a brushlike part of the apparatus. The apparatus is suitable for use in downhole tools. The bristles are bent in a first direction by being constrained in a hole facilitating movement in the opposite direction but preventing movement in the first direction.

[0001] This invention relates to a traction apparatus and especially butnot exclusively to a traction apparatus for use in a down hole toolwhich is adapted for operation in horizontal wells or bores.

[0002] Within the oil and petroleum industry there is a requirement todeploy and operate equipment along bores in open formation hole, steelcased hole and through tubular members such as marine risers and sub-seapipelines. In predominately vertical sections of well bores and risersthis is usually achieved by using smaller diameter tubular members suchas drill pipe, jointed tubing or coiled tubing as a string on which tohang the equipment. In many cases the use of steel cable (wire line),with or without electric conductors installed within it, is also common.All of these approaches rely on gravity to provide a force which assistsin deploying the equipment.

[0003] In the case of marine pipe lines which are generally horizontal,“pigs” which are basically pistons sealing against the pipe wall, areused to deploy and operate cleaning and inspection equipment, byhydraulically pumping them along the pipe, normally in one direction.

[0004] Within the oil and petroleum industry to date the requirement todeploy equipment has been fulfilled in these ways.

[0005] However, as oil and gas reserves become scarcer or depleted,methods for more efficient production are being developed.

[0006] In recent years horizontal drilling has proved to enhance greatlythe rate of production from wells producing in tight or depletedformation. Tight formations typically are hydrocarbon-bearing formationswith poor permeability, such as the Austin Chalk in the United Statedand the Danian chalk in the Danish Sector of the North Sea.

[0007] In these tight formations oil production rates have droppedrapidly when conventional wells have been drilled. This is due to thesmall section of producing formation open to the well bore.

[0008] However when the well bore has been drilled horizontally throughthe oil producing zones, the producing section of the hole is greatlyextended resulting in dramatic increases in production. This has alsoproved to be effective in depleted formations which have been producedfor some years and have dropped in production output.

[0009] However, horizontal drilling has many inherent difficulties, amajor one being that the forces of gravity are no longer working infavour of deploying and operating equipment within these long horizontalbores.

[0010] This basic change in well geometry has led to operations whichnormally could have been carried on wire line in a cost effective waynow being carried out by the use of stiff tubulars to deploy equipment,for example drill pipe and tubing conveyed logs which cost significantlymore than wire-line deployed logs.

[0011] Sub-sea and surface pipeline are also increasing in length andcomplexity and pig technology does not fully satisfy current and futureneeds. There is currently a need for a traction apparatus which can beused effectively in down-hole applications including horizontal bores.

[0012] According to the present invention there is provided tractionapparatus comprising; a body from which body extends at least onetraction member wherein said at least one traction member is adapted tobe urged against a traction surface against which traction is to beobtained, and wherein when said at least one traction member is urgedagainst such a surface it is adapted to move relatively freely in onedirection with respect to said surface, but substantially less freely inthe opposite direction.

[0013] Preferably, said at least one traction member is formed from aresilient material.

[0014] Preferably, said at least one traction member includes an endportion for contact with a traction surface.

[0015] Preferably, said body is elongate and said at least one tractionmember is adapted to be inclined so that it extends in a first axialdirection of the body as it extends between the body and a tractionsurface.

[0016] Preferably, the direction in which the traction member is adaptedto move preferentially is substantially opposed to the first axialdirection of the body.

[0017] Preferably, the system is for use in a bore and the tractionsurface comprises the inner wall of the bore.

[0018] Preferably, there is provided means to move the at least someportion of one or more of at least one traction members with respect tothe traction surface.

[0019] Preferably, said motion of the one or more traction membersallows propulsion of the body with respect to the traction surface.

[0020] Preferably, said propulsion is substantially in the direction inwhich the traction member moves preferentially with respect to thetraction surface

[0021] Preferably, the motion of the one or more traction members isprovided by applying a force with a component substantially parallel tothe direction of preferential movement of the at least one tractionmember.

[0022] Preferably, the motion of the one or more traction members isprovided by applying a force with a component substantiallyperpendicular to the direction of preferential movement of the at leastone traction member.

[0023] Motion may be provided to the one or more traction members byconnection to a rotary member having a first axis, which rotates about asecond axis which is not coincident with said first axis.

[0024] Preferably, said means to move the at least one traction membercomprises means to oscillate said at least one traction member.

[0025] Preferably, there are provided a plurality of traction members inclose proximity to each other, to form a discrete area of tractionmembers.

[0026] Preferably, at least two of the traction members in said discretearea are encapsulated together in a matrix of resilient material.

[0027] Preferably, where are provided a number of spaced apart, discreteareas of traction members.

[0028] Preferably, at least two discrete areas of traction members aremoved relative to each other.

[0029] Embodiments of the invention will now be described by way ofexample, with reference to accompanying drawings in which:

[0030]FIG. 1 shows an embodiment of traction apparatus in accordancewith the present invention incorporated into a down-hole tool;

[0031]FIG. 2a is a schematic cross sectional view of an alternativeembodiment of the present invention, which is hydraulically powered inuse;

[0032]FIG. 2b is a graph showing hydraulic fluid pressure versus timefor the embodiment of FIG. 2a in use;

[0033]FIG. 3 is a schematic cross sectional view of a furtheralternative embodiment of the present invention in use;

[0034]FIG. 4a is a schematic cross sectional view of a derail of theembodiment of FIG. 3 with a variation in configuration;

[0035]FIG. 4b is a schematic cross sectional view of part of a furthervariation of the embodiment of FIG. 3;

[0036]FIG. 4c is a cross sectional view showing a detail of theembodiment of FIG. 4b;

[0037]FIGS. 5a, 6 a and 7 a are schematic illustrations showing sideviews of the sequential positions of elements in a further embodiment ofthe present invention in use;

[0038]FIGS. 5b, 6 b and 7 b are schematic end views corresponding toFIGS. 5a, 6 a and 7 a, respectively;

[0039]FIGS. 8a and 8 b show schematically embodiments of brush sectionssuitable for use in embodiments of apparatus in accordance with thepresent invention; and

[0040]FIGS. 9a and 9 b show, respectively, a perspective view and across sectional view of an embodiment of a pig which includes tractionmembers.

[0041]FIG. 1 shows an embodiment of traction apparatus incorporated intoa down-hole tool 1. The down-hole tool comprises a body 2 which iselongate and which has a threaded front end portion 3 and a threadedrear end portion 4 to allow attachment into a tool string. (It should beappreciated that the terms “front end” and “rear end” are used forconvenience only and should not be considered limiting. Terms such as“in front” and “rearwards”, which will be used hereafter, are to beunderstood accordingly.)

[0042] The tool body is provided with brush portions of which three,designated 5 a, 5 b and 5 c are shown. Each brush portion 5 a, 5 b and 5c includes a number of brush sections and each brush section includes alarge number of resilient bristles which in this embodiment comprisetraction members, and which extend outwardly from the body 2. Thebristles thus have inner ends attached to the body and outer ends distalfrom the body.

[0043] If the down hole tool 1 is inserted front end first into a borewith a diameter larger than the diameter of the body 2 but slightlysmaller than the external diameter formed by the outer ends of thebristles, then the bristles will be bent back, by the contact with theinner wall of the bore, such that the outer ends of the bristles areaxially behind the inner ends of the bristles. Under these circumstancesthe outer ends of the bristles will contact the inner wall of the boreand will offer more resistance to rearward motion of the tool than toforward motion of the tool. The bristles therefore move preferentiallyin the forward direction as against the rearward direction. Preferredembodiments of the present invention employ the principle behind thisphenomenon to allow propulsion of a tool by providing relative movementor oscillation between two or more brush sections (ie two or more groupsof bristles constituting traction members).

[0044]FIG. 2a shows schematically a preferred embodiment of tractionapparatus in accordance with the present invention. The apparatuscomprises first to fifth sections 12 a to 12 e respectively.

[0045] The sections 12 a to 12 e are connected by a pipe 16 whichcarries hydraulic fluid. First to fourth resilient members 17 a to 17 dare provided between the first to fifth sections 12 a to 12 e.

[0046] The apparatus, as illustrated in FIG. 2a is provided within ahorizontal bore which has an inner wall 10 the surface of whichconstitutes a traction surface.

[0047] The second section 12 b of the apparatus will now be described indetail. The other sections 12 a, 12 c, 12 d, 12 e are similar instructure and function and will not be separately described in detail.

[0048] The second section 12 b includes a front portion 13 provided witha front brush section 19 and a rear portion provided with a rear brushportion 19. The brush portions 18, 19 are formed from resilient bristleswhich are, in use, deformed by contact with the inner wall 10 so thatthe outermost end of each bristle is to the rear of the inner most endof the bristle. The bristles thus constitute traction members which areadapted to move preferentially in one direction (to the right as shownin FIG. 2). The rear portion 14 is fixed around the pipe 16, is co-axialwith the pipe 16, and includes a larger diameter part 14 a and a smallerdiameter part 14 b. The smaller diameter part 14 b is forward of thelarger diameter part 14 a. Where the diameter changes between the largerdiameter part 14 a and the smaller diameter part 14 b an abutmentshoulder 14 c is formed.

[0049] The front portion 13 is able to move axially with respect to thepipe 16 and is sealed against the pipe 16 by a sliding seal 20. Thefront portion is cup shaped having a base part 13 a which contacts thepipe 16 and a cylindrical hollow part 13 b, extending rearward from thebase part 13 a, which is radially spaced apart from the pipe 16.

[0050] The inner diameter of the hollow part 13 b of the front portion13 is substantially the same as the outer diameter of the smallerdiameter part 14 b of the rear portion 14. The smaller diameter part 14b fits inside the hollow part 13 b and a sliding seal 15 is providedtherebetween. As the rear portion 14 is fixed with respect to the pipe16 and the front portion 13 is able to move axially with respect to thepipe 16, the hollow part 13 b is able to move axially with respect tothe smaller diameter part 14 b so as to cover more or less of thesmaller diameter part 14 b.

[0051] The hollow part 13 b has a longer axial length than the smallerdiameter part 14 b so that when the smaller diameter part 14 b iscompletely covered by the hollow part 13 b the rearmost end of thehollow part 13 b abuts the abutment shoulder 14 c but the forwardmostend of the smaller diameter part 14 b does not reach the base part 13 aof the front portion 13. A hydraulic fluid space 21 is formed betweenthe base part 13 a and the forwardmost end of the smaller diameter part14 b. A hydraulic fluid outlet 22 from the pipe 16 is provided to supplyfluid to the hydraulic fluid space 21.

[0052] In use, the hydraulic fluid pressure in the pipe 16 is increasedto force fluid into the hydraulic fluid space 21. This forces apart thefront portion 13 and the rear portion 14. Since the front portion 13 isless resistant to forward motion than the rear portion 14 is to rearwardmotion (because of the action of the brush portions 18, 19) this resultsin the front portion 13 being forced forward while the rear portion 14stays stationary. This results in axial lengthening of the hydraulicfluid space 21 and compression of the second resilient member 17 b.

[0053] The hydraulic fluid pressure in the pipe 16 is then reduced sothat the front portion 13 and the rear portion 14 are forced together bythe action of the resilient member 17 b, forcing hydraulic fluid fromthe hydraulic fluid space 21 via the outlet 22 into the pipe 16. As thefront portion 13 and the rear portion 14 are forced together theconsiderable resistance of the front portion 13 to rearward motionensures that the front portion remains substantially stationary withrespect to the, inner wall 10 of the bore, so the rear portion is forcedforwards with respect to the inner wall 10.

[0054] Each cycle of increase and decrease of fluid pressure in the pipe16 therefore results in the apparatus taking a “step” in the desireddirection along the bore. It should, of course, be appreciated thatalthough the above has been described with respect to only one section12 b of the apparatus of FIG. 2a, the other sections 12 a, 12 c, 12 d,12 e respond similarly to increases and decreases in fluid pressure.FIG. 2b shows how fluid pressure may be varied with time in order toobtain movement of the apparatus at a rate of about two steps persecond. (One PSI is equal to about 6.9×10³ Pa.)

[0055]FIG. 3 shows an alternative embodiment of a down-hole tool 1 aincluding traction apparatus according to the present invention suitablefor use on an electric line.

[0056]FIG. 4a schematically shows a detail of a variation of theembodiment of FIG. 3. The embodiment is illustrated as being within ahorizontal bore with an inner wall 10 a. The down-hole tool 1 a has afront end portion 3 a and a rear end portion 4 a.

[0057] The tool 1 a includes an electric motor 30 which drives an axle31 aligned axially along the centre of the tool 1 a. The axle 31 extendsaxially from the motor and is journaled at its end distal from the motor30 in a bearing 32.

[0058] Mounted on the axle 31, between the motor 30 and the bearing 32are first to sixth collars 41 to 46 which are inclined, at an angle awayfrom the normal, with respect to the axis of rotation of the axle 30.First to sixth annular brush portions 51 to 56 are mounted respectivelyon the first to sixth collars 41 to 46 via first to sixth annularbearings 61 to 66. For conciseness only one the first of thecollar-bearing-brush assemblies will be described in detail, but it willbe appreciated that the other assemblies correspond.

[0059] The collar 41 is fixed to an annular inner race 61 a of thebearing 61 which rotatably supports, via a plurality of rolling members61 b, an annular outer race 61 c of the bearing 61. Upon the outer race61 c of the bearing 61 is fixed an annular base part 51 a of the brushportion 51, which supports a plurality of bristles 51 b of brush portion51.

[0060] When the axle 31 is rotated by the motor 30 the first collarrotates so that its leading edge rotates about the axis of the axle 31.Because it is supported on the bearing 61 the first brush section 51 isnot caused to rotate by the rotation of the first collar 61. However, asthe collar rotates, the base part 51 a of the brush section 51 is movedso that any given point on the base part 51 a is moved one cyclebackwards and forwards relative to the axle for each rotation of theaxle.

[0061] The bristles 51 b of the first brush section 51 are thus forcedforwards and backwards, against the inner wall 10 a. The bristles movepreferentially in the forward direction and thus provide little reactionforce on the tool when moved forward against the inner wall 10 a. Incontrast, the bristles offer considerably more resistance when forced inthe rearwards direction and thus provide considerable reaction force onthe tool. Rotation of the axle 31 thus provides a net forward force topropel the tool in the forwards direction.

[0062] As illustrated in FIGS. 3 and 4a a number of brush sections 51 to56 are provided in order to provide greater traction than would beafforded by any one of the brush sections. It is preferable to have thebrush sections out of phase in order to distribute the thrustcircumferentially around the tool. In FIG. 3 each of the brush sectionsis shown as being 180 degrees out of phase with the adjacent brushsections, so that, as shown, the uppermost parts of the second, fourthand sixth brush sections 52, 54, 56 are forwardmost and the lowest partsof the first third and fifth brush sections 51, 53, 55 are forwardmost.In FIG. 4a a different phase distribution is illustrated. In particularthe forwardmost part of the third brush section 53 is the pars whichwould extend furthest out of the page (not shown), and the forwardmostpart of the fourth brush section 54 is the part which extends farthestinto the page, Thus in FIG. 4a each of the brush sections 51 to 56 is180 degrees out of phase with a first one of its neighbours, but eachbrush section which has two neighbours is also 90 degrees our of phasewith the second of its neighbours. Such an arrangement can provideimproved stability under traction. It should be noted that in FIG. 4a,because the planes of the third and fourth brush sections 53, 54 are nornormal to the page, more of the base parts 53 a, 54 a and bristles 53 b,54 b of the third and fourth brush sections 53, 54 can be seen than ofthe other brush sections.

[0063]FIG. 4b illustrates a variation of the embodiment of FIG. 3. FIG.4c shows in detail part of the embodiment is of FIG. 4b. As shown inFIG. 4b, first and second brush sections 57, 58 are mounted to an axle131 which can be rotated by a motor 130.

[0064] The brush sections 57, 58 each include a base section 57 a, 58 aand bristles 57 b, 58 b for engaging the inner wall 10 a.

[0065] Mounted to the axle 131 are first and second collars 47, 48corresponding generally to the collars 41 to 46 of the embodiment ofFIG. 3. Attached to the collars 47, 48 are first and second annularbearings 67, 68, corresponding generally to bearings 61 to 66 of theembodiment of FIG. 3 and each including an annular inner race 67 a, 68a, rolling members 67 b, 68 b and an annular outer race 67 c, 68 c.Attached to the respective outer races 67 c, 68 c of the bearings 67, 68are respective annular brush-base holders 67 d, 69 d, each adapted toreceive one or more brush base sections. Thus the brush base sections 57a, 58 a are not attached directly to the bearing outer races 67 c, 68 cbut are instead fitted into the brush base holders 67 d, 68 dfacilitating replacement of the brushes 57, 58.

[0066] Unlike the collars 41 to 46 of FIGS. 3 and 4a, in the embodimentof FIGS. 4b and 4 c the collars 47, 48 are mounted to the axle 131 byfixing pins 47 a, 48 a which extend through respective holes 47 b, 48 bwhich pass through the collars 47, 48 in a direction perpendicular tothe axle 131.

[0067] The embodiments of FIGS. 3 to 4 c thus provide traction apparatusin which traction, and corresponding motion, is provided by movingdifferent traction members (bristles in this embodiment) which arerigidly connected to each other (via the brush base parts) at differentvelocities in the axial direction, at any given time.

[0068]FIGS. 5a, 5 b, 6 a, 6 b, 7 a and 7 b illustrate the action of atraction device in which axial motion is provided by forcing tractionmembers in a radial direction with respect to a down-hole tool 1 b.

[0069] A down-hole tool 1 b is provided with first to eighth brushsections of which, for clarity in the drawings, the first and second 71,72 are shown in each of FIGS. 5a to 7 b, the third and fourth 73, 74 areshown in FIGS. 5b, 6 b and 7 b only, the fifth and sixth are shown inFIGS. 5a, 6 a and 7 a only, and the seventh and eighth are not shown.

[0070] Each of the brush sections 71 to 76 is attached to the main bodyof the down-hole tool 1 b by a respective arm member 81 to 86 which isradially extendable away from the main body of the tool 1 b.

[0071] FIGS 5 a and 5 b show the positions of the arm members 81 to 86and brush sections 71 to 76 in an inactive position in which all of thearms 81 to 86 are in their respective retracted positions and theoutermost ends of the brush sections 71 to 76 (that is the outermostends of the bristles) are in light contact with an inner wall 10 b of ahorizontal bore.

[0072]FIGS. 6a and 6 b show the positions of the arm members 81 to 86and brush sections 71 to 76 at a first stage in a traction cycle At thistime the arms 81 to 84 of the first to fourth brush sections 71 to 74are fully radially extended, forcing the bristles of the brush sections71 to 74 against the inner wall 10 b. This radial extension causes thebrush sections 71 to 74 to push against the inner wall 10 b in thebackwards direction, which applies a reaction force in the forwardsdirection (rightwards as shown in FIGS. 5a, 6 a, 7 a) on the body of thetool 1 b. The force will tend to move the body of the tool in theforwards direction. The broken lines in FIGS. 6a to 7 a correspond tothe positions of the brush sections 71 to 76 in FIGS. 5a and 5 b so thatthe forwards movement can be appreciated. As shown in FIG. 6a, at thispoint of the traction cycle the fifth and sixth arms 35, 86 and seventhand eighth arms (not shown) remain in their retracted position.

[0073]FIGS. 7a and 7 b show the positions of the arm members 81 to 86and brush sections 71 to 76 at a second point in the traction cycle. Atthis time the fifth and sixth arms 85 and 86 and the sixth and seventharms (non shown) are fully radially extended forcing the fifth and sixthbrush sections 75, 76 and the seventh and eighth brush sections (notshown) against the inner wall 10 b. As in the case of the first tofourth brush sections 71 to 74, described above, this applies a forceand corresponding movement to the body of the tool 1 a in the forwards(rightwards) direction. The first to fourth arms retract as the fifth toeighth arms extend so that, as shown in FIGS. 7a and 7 b the first tofourth arms are fully restricted when the fifth to eighth arms are fullyextended.

[0074] Continuous cycling between the position shown in FIGS. 6a, 6 band the position shown in FIGS. 7a, 7 b will provide a continuedpropulsive force on the body of the tool 1 a. Embodiments are envisagedin which traction members may be moved both axially and radially andeither the axial or radial movement might predominate.

[0075] One of many driving mechanisms may be used to extend and retractthe arms 81 to 86. For example, mechanical means such as a rotatingshaft with four-lobed cams could be used. Alternatively, a hydraulicsystem could be employed. As a further alternative an electro-mechanicalsystem could be used. It will also be appreciated that these and otherdriving mechanisms could be suitable for driving the motion of thetraction members in the other embodiments of the invention.

[0076] It will be appreciated that in certain embodiments of the presentinvention the traction members will, in equilibrium (that is when notcontacting a traction surface) be substantially perpendicular to theaxis of the traction apparatus. In such embodiments it is theconstriction of the traction members which effectively sets thepreferential direction of motion. In such embodiments it may be possibleto reverse the preferential direction of motion by overpulling the tool,ie by providing a sharp or jarring force. In other embodiments it may bemore appropriate to reverse the preferential direction by retracting andre-deploying the traction members.

[0077] It will be appreciated that although the preferred embodimentsdescribed herein are disclosed as including brushes in which thebristles constitute traction members, other types of traction membersmay be used provided they are able to contact the traction surface and,when in contact, move preferentially in one direction over the other. Itis preferred that the traction members are resilient elongate members,such as leaf springs or bristles. In the case of bristles it ispreferred that the bristles be encapsulated into a block of resilientmaterial in order to reduce wear.

[0078]FIGS. 8a and 8 b show embodiments of first and second brushsection 180 a, 180 b, respectively.

[0079]FIG. 8a shows a round brush section 180 a having a number ofbristles 182 a encapsulated in a matrix 184 a of urethane or othersuitably resilient material. The bristles 182 a are supported in a brushbase section 186 a comprising a generally cylindrical metal casing forholding the bristle bases. A threaded connection portion 188 a isprovided facilitating easy fitting and replacement. Other types ofconnection could, of course, be used. In this embodiment only thebristle tips are uncovered by the matrix 184 a.

[0080]FIG. 8b shows a rectangular brush section 180 b having a number ofbristles 182 b encapsulated in a rubber matrix 184 b. The bristles 182 bare supported in a brush base 186 b which consists of a block offoundation material. A connection portion 188 b is provided. In thisembodiment a predetermined length of the bristles 182 b extends from theouter end of the rubber matrix 184 b.

[0081] The contact of the traction members on the traction surface isimportant in order lo obtain preferential movement in one direction. Inpreferred embodiments it is desirable that the ends or tips of thetraction members engage the traction surface. The length of the tractionmembers is therefore important, since if a traction member is too shortit might not reach the traction surface, and if the traction member istoo long it might be an axial surface of the traction member, ratherthan the tip of the traction member, which engages the traction onsurface. In practice, for many types of traction member, a range oflengths provide an acceptable result. Choice of length may be ofparticular importance in embodiments such as those of FIGS. 3 to 7 b inwhich the distance between the innermost end of the traction member andthe traction surface varies during operation of the apparatus. It isdesirable that an effective length of traction member is maintained atall times.

[0082] It should be appreciated that the distribution of the tractionmembers may be varied according to the circumstances. It is desirable,but not essential, to have traction members diametrically opposed on theapparatus in order to maintain good stability. Traction members may (orgroups of traction members) may be axially or circumferentially spacedas desired. The number and properties of the traction members may alsobe varied according to the circumstances.

[0083]FIGS. 9a and 9 b show a pig 90 including bristles 92 encapsulatedin a matrix 94. The bristles 92 are set into an annular bristle base 96made of a foundation material, in an inclined manner. Outer zips 92 a ofthe bristles 92 extend out of the matrix 94 for engaging the inner wall10 a.

[0084] In use, the pig 90 can be moved to a desired position, forexample on a drill string, by application of continuous fluid or gaspressure on the rearward side (the leftward side as shown in FIG. 9b).When the progress of the pig is impeded such that the continuouspressure is insufficient to move the pig in the desired direction, thepig can be oscillated in order to provide traction because of thepreferential motion of the bristle tips 92 a against the wall 10 a inthe forward direction.

[0085] Modifications and improvements may be incorporated withoutdeparting from the scope of the invention.

1. A traction apparatus comprising: a body from which body extends atleast one traction member wherein said at least one traction member isadapted to be urged against a traction surface against which traction isto be obtained, and wherein when said at least one traction member isurged against such a surface it is adapted to move relatively freely inone direction with respect to said surface, but substantially lessfreely in the opposite direction.
 2. A traction apparatus as claimed inclaim 1 wherein said at least one traction member is formed from aresilient material.
 3. A traction apparatus as claimed in eitherpreceding claim wherein said at least one traction member includes anend portion for contact with a traction surface.
 4. A traction apparatusas claimed in any preceding claim wherein said body is elongate andwherein said at least one traction member is adapted to be inclined sothat it extends in a first axial direction of the body as it extendsbetween the body and a traction surface.
 5. A traction apparatus asclaimed in claim 4 wherein the direction in which the traction member isadapted to move preferentially is substantially opposed to the firstaxial direction of the body.
 6. A traction apparatus as claimed in anypreceding claim wherein the system is for use in a bore and the tractionsurface comprises the inner wall of the bore.
 7. A traction apparatus asclaimed in any preceding claim wherein there is provided means to movethe at least some portion of one or more of at least one tractionmembers with respect to the traction surface.
 8. A traction apparatus asclaimed in claim 7 wherein said motion of the one or more tractionmembers allows propulsion of the body with respect to the tractionsurface.
 9. A traction apparatus as claimed in claim 8 wherein saidpropulsion is substantially in the direction in which the tractionmember moves preferentially with respect to the traction surface.
 10. Atraction apparatus as claimed in any of claims 7 to 9 wherein the motionof the one or more traction members is provided by applying a force witha component substantially parallel to the direction of preferentialmovement of the at least one traction member.
 11. A traction apparatusas claimed in any of claims 7 to 10 wherein the motion of the one ormore traction members is provided by applying a force with a componentsubstantially perpendicular to the direction of preferential movement ofthe at least one traction member.
 12. A traction apparatus as claimed inany of claims 7 to 11 wherein motion is provided to the one or moretraction members by connection to a rotary member having a first axis,which rotates about a second axis which is not coincident with saidfirst axis.
 13. A traction apparatus as claimed in any of claims 7 to 12wherein said means to move the at least one traction member comprisesmeans to oscillate said at least one traction member.
 14. A tractionapparatus as claimed in any preceding claim wherein there are provided aplurality of traction members in close proximity to each other, to forma discrete area of traction members.
 15. A traction apparatus as claimedin claim 14 wherein at least two of the traction members in saiddiscrete area are encapsulated together in a matrix of resilientmaterial.
 16. A traction apparatus as claimed in either of claims 14 or15 wherein there are provided a number of spaced apart, discrete areasof traction members.
 17. A traction apparatus as claimed in claim 16wherein at least two discrete areas of traction members are movedrelative to each other.